Ketone
A ketone has the carbonyl group (C=O) bonded to two other carbons — never at the end of the chain (that would be an aldehyde). It's the functional group behind common solvents like acetone.
General formula
R–CO–R'
Naming rule
Name = main chain + suffix -one, with the carbonyl's locant when there's ambiguity (e.g., pentan-2-one vs. pentan-3-one).
How to name it with IUPAC
Use this sequence to move from the structure to the systematic name:
- Choose the chain containing the carbonyl bonded to two carbons.
- Number to give the carbonyl the lowest locant and use -one.
- CH₃COCH₂CH₃ = butan-2-one: carbonyl at C2.
CH₃COCH₂CH₃ = butan-2-one: carbonyl at C2.
Examples
| Name | Formula |
|---|---|
| Propanone (acetone) | (CH₃)₂CO |
| Butan-2-one | CH₃COC₂H₅ |
| Pentan-2-one | CH₃CO(CH₂)₂CH₃ |
| Cyclohexanone | C₆H₁₀O, ring |
Visual examples
See how the functional group appears inside the chain. Compare the drawings with the formulas in the table to practice visual recognition.
Chemical reading
The carbonyl lies between two carbons. Ketones accept hydrogen bonds but have no O–H bond to donate them.
Properties and applications
Propanone (acetone) is a laboratory and cleaning solvent; reduction gives a secondary alcohol.
- A terminal carbonyl with H is an aldehyde; an internal carbonyl is a ketone. CH₃COCH₂CH₃ is butan-2-one.
- Compare polarity, chain size, and hydrogen bonding before predicting physical properties.